Process for photogravure



Jan. 17, 1928. l 656 843 E. STRAUB PROCESS FOR PHOTQGRAVURE Filed March 26, 1926 Q7 AI B321. &\ \\\& 1

@N C, FLA TE EMULSION Fig. 2.

ZIM Q PLATE W AFTER EXPOSURE A V /j-! A l HAND DEVELOPMENT g BA RE sumces OF ZINC I Zuvc PLATE N BARE SURFACES HELL/I C- PLACED OF ZINC .SHELLAc i INSOLUBL-E EMULSION xposme 5: :I NNOVED 5 Ex P0550 PA RTS d @{ET'GHED avAeap Fig,6. {m W Patented Jan. 17, 1928.

UNITED STATES PATENT OFF-ICE.

EMILE BTRAUB, OF PARIS, FRANCE, ASSIGNOR T JEAN GRIFFITHS, 0F PARIS,

FRANCE.

PROCESS FOR PHOTOGRAVURE.

Application filed March 26, 1926, Serial No. 97,803, and in France February 10, 1928.

The invention relates to improvements in processes for photogravure upon zinc plates for printing purposes.

The said improvements have for their oba jects the composition of the products and the method of utilizing the same.

As a whole, my said process differs from the known processes by the composition of the mixtures and also from the fact that the m zinc plate does not require to be treated in different baths. In this manner I obtain the following advantages.

The operator can now develop the plate with great accuracy, stopping the action when the image appears or further treating the parts of the image which require a greater devolpment. Since it will now suffice to rub the plate with the various products which can be preliminarily prepared,

an no great installation is required, and the op erations can be performed in an ordinary room upon a small table, and by a person possessing little skill.

Tn the known processes, the drawing or at design must be made upon a special paper,

but my said process provides for the copying or an original, whether printed, written or drawn, upon any kind of paper, and even of the thickness of Bristol board. It is not 31 necessary that the lines of the original shall be perfectly black.

The following description taken in connection with the accompanying drawing clearly shows the manner in which my said process is carried into eifect, as well as the composition of the products in use.

Fig. 1 shows the zinc plate covered with the emulsion used.

Fig. 2, shows the zinc plate. covered with n the emulsion and with the design to be reproduced.

Fig. 3 shows the zinc plate covered with emulsion after development and after the soluble parts have been dissolved.

Fig. 4 shows the zinc plate with a gum covering the bare spots of the zinc shown in Fig. 8.

Fig. 5 shows the zinc plate with the emulsion removed and the parts inked.

Fig. 6 shows the zinc plate ready for use in printing.

The plate is first cleaned by rubbing it with rather coarse powdered pumice stone and with dilute sulphuric acid (5 grams per 500 grams Water).

1st operation-The plate is covered with a sensitive layer, and for this purpose a smallquantlty of the following mixture is spread upon the zinc plate with a pad: Water, 125 grams, gum arabic 30 grams, ammonium bichromate 6 grams.

The zinc is then dr1ed by means of hot air electric dryer. The drawing (or letter) to be reproduced, which has been formed upon any kind of paper, is pressed against the z 1nc plate, and the whole is exposed to the light, using for instance a strong incandescent lamp. In Fig. 1, a indicates the zinc plate, 6 the sensitive layer, and in Fig. 2 the object to be reproduced is indicated by c, the parts in black being indicated in black.

2nd operation-A few drops of the following solution: Water 150 grams, glycerin 400 grams, acetic acid, crystallizable 25 0.0., are placed upon the zinc plate, and it is then rubbed with a soft pad (printers blanket) until the image appears, bearing particularly on the parts which appear more slowly. The plate is then wiped with a soft cloth. Fig. 3 represents the zinc plate with emulslon after development, the soluble parts (porresponding to the black parts of the design) are indicated by (Z and the insoluble parts (corresponding to the light parts of the design) by 6.

3rd operatiou.-The plate is washed with a few drops of the following solution: Alco.

hol, denatured (90 per cent) 470 c.c.; acetic acid, commercial 30 cc, and this will complete the development, even slightly attacking the zinc in the parts unacted upon by the light (blacks of the drawing). This washing removes the remainder of the emulsion which was not altered by the action of the light.

4th operation-A small quantity of the,

following solution: Alcohol, denatured (95 per cent) 47 5 c.c.; shellac, brown 25 grams, is spread upon the zinc with a soft cloth, rubbing in such manner that the shellac will penetrate into the parts of the plate where the zinc is left bare (blacks of the drawing). The plate is then dried with an electric dryer employing cold air, and is then washed in ordinary water and dried. In Fig. 4 the gummed parts are indicated by f. The gum old upon the zinc, that is the parts covered by the shellac, and not upon the emulsion which always remains somewhat moist.

6th operation-The zinc plate is rubbed over with a small amourit of talcum powder to dry the ink.

7th operation.--The insoluble emulsion formed upon the plate is removed by a soft cloth, and I employ the following solution for this removal: Hydrochloric acid 25 c.c.,'

water 1 liter. Should there be any defects in the drawing, these are to be retouched. In Fig. 5 it is seen that all the emulsion is lifted from the zinc-plate and that there remains only the inked parts indicated by f.

8th operation.-In order to attack or to etch the plate in the parts which are not to be inked, the plate is coated with a brush made of textile fabric, with the following solution: Hydrochloric acid 0.0., nitric acid 35 c.c., phosphoric acid 20 c.c., gallic acid 4 grain. The zinc plate is then wiped and dried, and it is now ready for the printing process. The press, or a roller machine, can produce any desired number of copies of the original drawing or letter. In Fig. 6, the parts attacked by the acid and roughened are indicated by g, while the smooth parts which retain the ink are indicated by h.

Obviously, the proportions above indicated for the composition of the roducts are susceptible of all necessary mod cations, without departing from the invention.

Having so described my saidv invention and in what manner it is performed, I declare that what I claim is- The process for forming etched plates for use in printing which comprises applying to the plate a thin layer of a solution of gum arabic and ammonium bichromate, drying it and exposing the surface to the action of light through the object to be reproduced, rubbing the exposed plate with a solution of glycerine, water and acetic acid until the image appears, washing the plate thereafter with a solution of alcohol and acetic acid, applying to the plate a solution of a quickly drying varnish and rubbing in order to make the varnish penetrate the parts of the plate where the plate is bare, thereafter drying and washing and inking it with printing ink, thereafter removing the light affected layer with dilute hydrochloric acid and etching the exposed parts of the plate.

In testimony whereof, I have signed my name to this specification at Paris, this 10th day of March, 1926.

EMILE STRAUB. 

